This invention relates to a torque limiting mechanism for use in a drive system.
The invention has application, for example, to the drive mechanism of a cash dispenser unit of an automated teller machine (ATM) in which there is provided a currency note picking apparatus for extracting notes from one or more currency cassettes mounted in the cash dispenser unit. As is well known, in operation of an ATM a user inserts a customer identifying card into the machine and then enters certain data (such as codes, quantity of currency required or to be paid in, type of transaction, etc.) upon one or more keyboards associated with the machine. The machine will then process the transaction, update the user's account to reflect the current transaction, dispense cash, when requested, extracted from one or more currency cassettes, and return the card to the user as part of a routine operation.
One known kind of cash dispenser unit of an ATM includes a currency note pick mechanism which incorporates pivotably mounted pick arms disposed adjacent an associated currency cassette, the pick arms being arranged to draw part of an end note of a stack of notes in the cassette away from the remainder of the stack, by applying suction force to the end note, and to position said part for engagement by transport means arranged to remove the end note from the cassette. In a typical cash dispensing operation, the transport means feed a plurality of notes one by one to note stacking means where the notes are stacked in a bundle, the bundle of notes then being fed to an output station, represented by a cash exit slot, for collection by a user of the ATM.
It can sometimes happen that, in operation of a currency note pick mechanism, due to a malfunction of the mechanism a so-called gulp feed occurs in which a plurality of currency notes, instead of a single note, are erroneously picked from the cassette in one cycle of operation of the pick mechanism. Such a malfunction may occur, for example, if the cassette has been loaded incorrectly, or if a note pusher mechanism in the cassette has become jammed. When there occurs a gulp feed involving more than a critical number of notes, the gear wheels driving the note transport means may be highly stressed and one or more gear wheels may fail. Even though only one gear wheel may fail as a result of a gulp feed, all other gears in the driving system will have been so highly stressed that it is likely that further use will soon result in more failures. Thus, once such a gulp feed has occurred, it is likely that a major gear change will be required before the pick mechanism can be used again with any confidence.